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I have a WMS layer in QGIS and I want to select and extract certain features in order to vectorize them and perform clipping with other vector layers. Is there any way of doing this? I don't have access to the WMS source files.

  • Depending on the WMS (software and provider configuration dependent. etc.), a GetFeatureInfo request might give some geometry for a feature, you could also check whether there is also a simple feature WFS available in the background. – nmtoken Jan 29 at 12:32
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No you can't (in any sensible way). WMS services serve images not data (see here) to the user. While you could use some fancy image processing software to edit the images I don't think that's what you're after. There is almost certainly a better way to achieve whatever objective you're aiming at.

One way or another you're going to want to get hold of the vector data which has been used to create the map you're working from. If it's open data that ought to be easy. If it's not, then you're going to need to think about copyright anyway - and there's probably a better solution by looking instead at a source of open data, or a source of closed data which you have the right to use.

There are some more advanced options with WMS which are beyond my knowledge - but they might offer some workarounds if you're stuck with using a particular WMS service. See this question.

  • So would the most feasible way of extracting information be to manually draw a vector polygon over the feature in the WMS layer? – Steffan Clent Davies Jan 29 at 11:56
  • Depending on the scale you could export the current map-display as an image, load it and use the raster calculator and contour-tool to extract the desired features. Though that still might require some manual work afterwards. – Erik Jan 29 at 12:09
  • What's sensible/feasible will depend on your general GIS knowledge/skills, the scale of the task, and the software available. That question is very difficult to answer without knowing what you are trying to do. What kind of 'features' are you wanting to create vectors for? Are you working from a simple map? If you want to map shapes you need polygons, roads would be polygons or lines depending on scale, other features might be points or polygons depending on scale too. Are you REALLY sure that the only way forward is to work from this WMS service? – Rostranimin Jan 29 at 13:21
  • Steffan, I've added a link to a more advanced question/answer about WMS which describes some more advanced WMS abilities that I wasn't aware of. I'm not sure they will help you, but it's worth a look if you're stuck with working from a particular WMS service (with no options to get the actual data). – Rostranimin Jan 30 at 10:08
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To add a bit to the former answer,
some ArcGIS services serve WFS as well as WMS, this is visible in QGIS.
This is not supposed to happen, but it never hurts to test if the WMS you want to access has that capability.
you can try adding the service using the data source manager's arcgis wfs using the same address. i.e. using a url ending in mapserver and not featureserver.

I wrote a short guide about that here along with the note about ArcGIS services and some examples
(https://ags.iplan.gov.il/arcgis/rest/services/PlanningPublic/Xplan/MapServer for example works that way even though they set it up as only a map service)

as stated above you should always mind the license under which the data provided.

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